^8mm steel axle (later versions were upgraded to threaded 12mm)
Dexter, you know not what you have done.
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We’ll isn’t that by design why that happened. lol Doesn’t seem like there was that many that actually were damaged though or was there?
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Fortunately it was a test version being ridden by the designer and to my understanding only the upgraded 12mm designs were shipped out to customers.
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This.
Feel like the 8mm axle broke for different reasons.
Gonna upset Brian
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summary:
peak pounds force on 8mm axle from torque (75kv, 120a motor): 855.1lbs
pounds force on axle from normal force (200lb vehicle, 4 wheels): 50lbs
assumptions: roughly 75kv 120a motor current, 8mm diameter axle
axle radius: 4mm
torque per amp: 0.127nm/a = 60/(2 * pi * 75kv)
total torque: 15.24nm = 120a * 0.127nm/a
total force at axle: 3817.5 newtons = 15.27nm / 0.004 meters axle radius
total force at axle (pounds force): 855lbs force = 3817.5n * 0.224 pound force per newton
^ the force applied to the axle from torque from the motor was a factor of 17 times greater than the normal force caused by someone standing on the board.
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You’re still talking about an 8mm axle that didn’t go into production?
years later folks still don’t agree on the root cause of the failure… some claim leverage
What’s the normal force from someone riding? Down curbs, over large tracks, doing ollie’s and power slides?
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that’s a bit more tricky to calculate because some of the energy will be absorbed by the tire, and it depends on the rider’s velocity, size of the bump & radius of the wheel, or drop distance if you’re getting air, and the weight of the rider.
I just don’t think saying
Is relivent then. We don’t just stand on skateboards.
17x more sounds like alot but the base it’s really reflective of what trucks normally go through.
keep in mind it was reported to me the 8mm hub motor axle failure occurred while the rider was accelerating from a low speed in a flat, smooth area
this is a true color image with increased saturation & contrast and I personally interpret the bluish, curved sections of the failure pattern as resulting from torque, not leverage.
(right side up)
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How do we know that the axle didn’t already have fatigue damage?
I’ve broken few axles. All bent first before snapping so I knew it was coming.
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Well the truck was only a few weeks old and I’ve never known the rider to do any jumps or other high impact skateboard tricks.
I broke one after 5 weeks. And it was strictly a A - B low power esk8. Bike paths and sidewalks only.
But I blame that on impurities in the case.
Still, whatever stress any 8mm truck would ordinarily go through from beginner or advanced riding, the motor puts an additional force above and beyond that which in this case was in the neighborhood of 855lbs, or ~17x the ~50lbs normal force per wheel.
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What about the bearing thing dexter pointed out?
I don’t know since every action requires and equal an opposite reaction. If the wheel accelerates in one direction, a force must be applied to something in the opposite direction. In the case I’ve described the rotor is pushing against the stator via magnetic forces, the stator is attached to the axle or truck.
The stator axle shouldn’t be connected to the axle anyways. It should be rolling on bearings if you’re connecting it to an axle. That should be pretty obvious.
Not sure why you are beating the 8mm axle issue as that’s not even an issue anymore since it’s been upgraded.
Seems like you’re beating up on old news.There was only one prototype of that available so why so much issue on an 8mm axle that doesn’t even exist.
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I’d imagine some of that force is taken up by the bearing before the axle.